Kiln



V. J. AZBE Sept. 29, 1953 KILN 4 Sheets-Sheet l Filed July 25, 1949Sept. 29, 1953 v, J, AZBE 2,653,809

KILN

Filed July 23 1949 irv Sheets-Sheet 2 4 Sheets-Sheet 3 V. J. AZBE KILNSept. 29, 1953 Filed July 25, 1949 l V. J. AZBE sept. 29, 1953 KILN . nJ l a J O1' 000 l 4. Sheets-Sheet 4 Filed July 23 1949 Patented Sept.29, 1953 KILN Victor J. Azbe, Webster Groves, Mo., assigner to AzbeCorporation, Clayton, Mo., a corporation of Missouri Application July23, 1949, Serial No. 106,376

7 Claims. l

This invention relates to kilns, and more particularly to rotary kilnsfor burning lime, cement, magnesite, et cetera.

Brieiiy, the invention comprises the combination of -a rotary kilnelement (including endwise circular sections and a longitudinallysectored part extending into the calcining zone) with a combinationstone preheater and dust collector at the inlet; a stationary shaft atthe outlet comprising a finishing and -a cooling zone; and ring means atthe outlet of the rotary element which includes recirculating heatrecuperator means supplied both from the inlet and from the stationaryshaft. The invention also includes iinprovements per se in theconstituent elements of the stated. combination. By means of theinvention, a smaller-sized kiln of lower iirst cost and upkeep may beemployed for a given capacity operating at a much higher thermaleiciency and at a considerably lower temperature peak than heretofore.The lower temperature peak allows for more effective heat insulationwithout in-` curring refractory failure, scale adhesions and ringproblems in the rotary elements. The in- Vention also provides a kiln ofthe rotary type which is more easily controlled andy less critical inits stone size acceptance than was the case with prior rotary kilns andone in which the dust hazard usually associated with rotary kilns isreduced. Moreover, a superior but more economical product is obtained.Other features will be in part obvious and in part pointed outhereinafter. f f

The invention accordingly comprises the elements and combinations ofelements, features of construction, and arrangements of parts which willbe exemplified in the structures hereinafter described, and the scope ofthe application oi which will be indicated in the following claims.

Fig. 1 is a diagrammatic side elevation on a reduced scale, showing theinvention in gross;

Fig. 2 is a chart of gas temperatures (upper curve) and per cent of heattransferred from gas to charge (lower curve), being longitudinallyrelated to Fig. l so as to indicate kconditions throughout the kiln;

Fig. 3 is a detailed axial section of the left end inlet portions ofFig. 1, showing a stone Contact preheater and dust collector;

Fig. 4 is a detailed axial section (parts being broken away)illustrating the intermediate ro'- tary portion of the kiln;

Fig. k5 is a detailed axial section of the righthand portion of Fig. l,showing certain firing, finishing and recuperating cooling apparatus;

Figs. 11 and 12 are views similar to Fig. l0 eX-` cept that theyillustrate corresponding conditions at successive angles of operation inthe rotary kiln elements employed in the invention, being taken on lineI-II of Fig. 4; and,

Fig. 13 is a detailed section taken on line I3-I 3 of Fig. 5.

Similar reference characters indicate corresponding parts throughout theseveral views of the drawings.

Referring now more particularly to Fig. 1, the board outlines of theapparatus will iirst be described. These comprise a sloping rotary drumsection I, consisting of a steel tube 3 lined withY refractory and heatinsulating material 5. This tube 3 is carried by rings 'I riding onsupporting rollers 9. This drum also carries a ring gear H driven by apinion I3, the latter being driven from a motor I5 through aspeed-reduction gear box At the upper open inlet end I9 of the drum l islocated a heat economizer and dust chamber 2I. In the dust chamber is astone preheater cone 23rwhich receives stone or like material to beburned from a bunker 25. The Stone finds its way from the bunker 25through the preheater 23 to the open end I9 of the drum I, in a mannerto be detailed below.

At its opposite or lower end, the drum I has an outlet 2l leading into aring hood 29, surrounding ya burner assembly 3|. The firing hood formsthe top of a vertical shaft 33 constituting (Fig. 5) an upper finishingzone 2 and a lower cooling zone 4 through which passes the not quitefinished discharge from the drum I. The finally finished and cooledproduct is finally discharged through a` Variable capacity feeder 35 toa pressurized outlet chamber 3l from which it escapes through an airlock 39 to an outside conveyor 4I Recirculating heat economizer means intwo parts are employed. One of these is the firing khood 29 which, aswill be shown below, receives air that has been warmed in the coolingzone l of the shaft 33 but which by-passes the finishing zone 2. Thehood also receives gases from the zone 2. The hood delivers its warmgases to the outlet 21 of the drum I, these being injected into the drumby the discharge from the burner assembly 3|. The second part of therecirculating system comprises a. recirculating pipe 43 leading from thechamber 2| and to the burner assembly through a recirculating fan 45.

Details of the elements broadly outlined above are as follows,startingwith the drum This drum has an open section 41 near its upperoutlet I9 wherein preheating takes place. The pre-- heating zone isindicated at 53. At the other end of this open section are spiral fins49 (see also Figs. 4 and 8). At the lower: endof the drum is a secondopen sectionv5|,.wherein fuel. carburetion takes place. Between the fins49 and the section 5| is a divided or-quadrated. section which includesa part of the preheating zone 53 and a calcining zone 55. The quadratingconstruction is indicated generally by the numeral 51 and is shown inparticular in Figs. ll and 12. It is constituted by cruciform refrac-vtory walls 59, which divide the section 51 into four axial sectors intowhich under rotation: of the drum the charge is distributed by the'spiral fins 49. The effect of these sectors upon the charge may be notedbycomparing Fig. l with Figs. 11 and 12. Fig. 10 shows how a charge actsin an ordinary non-quadrated rotary kiln. As rotation takes place(anticlockwise) there is an anticlockwise rolling action applied to thelcharge. This causes the formation of' an outer stratification of coarseparticles 6|, which in turn surround a stratification of mixed particlesB3, which in turn surround a central stratication of fine particles 65.Thus the ner the particles are, the more they are blocked off from thereception of heat. Heretofore, high temperatures were required in rotarykilns applied for long periods in order to penetrate the stratificationsin order to complete theY calcining of the fine particles. The increasedtime needed required an increase in theV length of the drum and the hightemperatures precluded carrying any quadrating structure into thecalcining zone. As demonstrated in Figs. 11 and 12, all of thecategories of coarse particles 6|, mixed particles 83 and fine particles65 are tumbled, sol that at some time or times during the rotary processthey become exposedto radiant heat.

At its left end the drum I carries an annular end seal 61 with the dustchamber 2|, the seal being provided with a negative internal pressure bybleeding to the recirculating duct 43 via a connection 69 wherein thereis a control valve 1|. At this end the drum also carries an inwardlydirected stone spill dam |09. Atits other (lower) end, there is alsoarranged a seal 13 between the drum I and the firing hood 29. At thispoint the refractory is stepped inwardly to form a dam 15 beyond whichis a nose ring 11. This ring is interiorly channel-shaped and mayinclude openings or foraminations 19, to act as a classifier. However,this classifier function is not always necessary, in which event thenose ring is made without openings through its channel section.

Referring to further details of the dust chamber 2|, it will be seen toinclude a dust hopper 3| at the bottom of which is a gate 33; also astone-spill hopper 85 at the bottom of which is a gate 81. The preheater23 is in the upper part of the dust chamber 2| and includes an i-nternalspreader hood 89, which causes the rock entering from the rock supplybunker 25 to assume a surface of repose such as indicated at 9|. Thissurface is within a conical portion 93, wherein are louvers throughwhich hot gases may enter the interior mass of stone. This spreads therock over the louvers. These gases traverse the stone, which acts as afilter to settle much of the entrained dust. Heat is also transferredfrom the gases to the stone for initial preheating. The filtered gasesare drawn off through an exhaust duct 91 which is connected to thespreader hood B9, being pulled off by an exhaust fan 99. A by-pass duct|9| connects the chamber 2| with the duct 91. Contml' dampers|031and1|05 are used in the ducts 91 and. IUI.. It willlbe noted thatnot all of the gases leavethe chamber 2| via pipes 91 and |0|, but thatsome of them are drawn off over the hot gas recirculating duct 43. Thefunction of this will appear.

At the lower end of the cone 93 is an outlet pipe |01- to which ispivoted a feed spoutA controlled in position by adjustable suspensionmeans I3. The spout may take a lowered position shown in solid lines, ora raised position Shown in dotted lines. In the lower position, thelevel of the stone in the open section 41 will be less than it is in theraised position, since when the level of the stone reaches the outlet ofthe feed spout, no more stone will flow until this levelis reduced bythe .stone` proceeding down the section 41.

Referring now to the details of the stationary shaft 33 at the loweropening outlet end ofthe drum I, it comprises the ring hood 29 aroundthe nose ring 11. Below the outlet of the drum I the shaft isconstructed as shown in Fig. 6, wherein it is divided into sixdownwardly extending chambers |I5 having tapered lower outlets I |1. Theexact number of these is optional. They are viewed from the bottom inFig. 7. They carry airinlet louvres 6 and are surrounded by an airplenum chamber 8. Under the outlets ||1 are doorsk |I9 carriedadjustably upon reciprocating bars |2I, the latter being carried inbearings |23 and being joined by a crosshead |25. The crosshead |25, andconsequently the rods I2| and doors ||9, are reciprocated byconnectionsA |21 with cranks |29 driven from a suitable actuator |3|.Thus through adjustment of the doors II9 on the rods |2| and thereciprocation of the rods, the finished material may be drawn from therespective chambers I|5, thereby providing a variable capacity outputfor each of these. Below the outlets ||1 is a conveyor belt |33 whichdelivers all of the material withdrawn from the chambers ||5 to theoutlet 39 from whence it is delivered to the belt 4| for delivery tostorage. In the outlet 39 is an air lock as illustrated in Fig. 13,which consists of a rotary vane member |35 in a. cylindric passage |31.This member upon rotation passes solid material out without permittingcontinuous ow of air. The reason for this air lock is that the outletsI|1 are surrounded by an air-pressure plenum chamber |39 from which itis desired to allow air to escape only by passage through the openings|I1 to the chambers ||5 as the finished material shakes therefrom. Thisair is obtained through an air pressure connection |4| (in which is acontrol valve |42) with an air mani fold |43 supplied by a cooling fan|45. The manifold |43 also has connections |41 (in which are controlvalves |48) which supply cooling air individually to the lower ends ofthe plenum chamber 8. This air enters the louvers 6 and cools thecharges as they approach their outlet gates. As will be shown, it isdesired to have a heat-soaking finishing operation occur at the upperends of the chambers I I5 and to have a portion of the cooling airby-pass the resulting finishing zone. This is accomplished by means ofhorizontal offtake pipes |49 across the pas-y sages H5 at anintermediate point thereof, each having lower openings |5I and a controlvalve |53. These pipes include risers |55 which are reconnected atpoints near the firing hood, as shown at |51. Thus the region below thepipes |49 constitutes a cooling zone and a substantial portion (but notall) of the air used in that zone by-passes the finishing zone above thepipes |49. The remainder passes through the finishing zone. All of theair finally enters the firing hood 29 and most of it is directlyinjected as secondary air along with fuel into the carbureting section5I of the drum I. Some is drawn off through the recirculation duct 43via offtake |61, to be used as primary air in the burner 3|.

The burner assembly 3| includes a fiaring fuel nozzle |59 appropriate tothe fuel being used, such as natural or artificial gas, oil, powderedcoal, etc. This nozzle is surrounded by a fiaring manifold jacket ISIsupplied with hot recirculating gas over line |63. In line |63 is arecirculating fan 45 drawing hot gases from the recirculating duct 43.Thus both spent gases (from the dust chamber) and some air (from thefiring hood) are delivered to the manifold IBI by the fan |65.Additional air for temperature control may be obtained from bleeders |69controlled by valves |1I. The flare of the burner provides a wide-angleentry of combustible into the drum I, wherein it spirals to aidcarburetion. If spirallingr is not inherent suitable spiral baffles maybe incorporated between the nozzle |59 and the manifold jacket I6I.While the walls 59 stop spiralling action of the gases, it is reinstatedthe section 41 by the spiral fins 49. The flaring dam coopcrates withthe flaring burner to carburet,` and with the adjustable feed spout IIImaintains a desired level of material passing out of the drum I.

Since some scale is encountered in the material leaving the drum I,agitator grates |13 are provided, which screen out scalematerial andsend it toward a clean-out door |15 for delivery to a suitable hopper|11 via chute |19.

Operation is as follows:

The drum I is rotated and the feed spout III adjusted to the depth ofcharge to be carried in the inlet section 41. Stone (or any similarmaterial to be burned or calcined) leaves the supply by gravity and isspread into the shape 9| (within the cone 93) by the spreader hood 89.Here it is preliminarily preheated by hot gases traversing it, while itacts as a dust filter for the gases. From here it descends the spout IIIand rotation of the drum I carries it down the slope of the open section41 at the end of which it is picked up by the spirals 49 and distributedamongst the sector-shaped passages determined by the quadrating walls59. During this stage the material is further preheated. It thenproceeds down the walls, being tumbled and adequately brought to thesurface at intervals, passing through the hot calcining zone (into whichthe walls 59 extend) and finally entering the open carbureting section5|. Its level is maintained by the eleva-*l tion of spout |I| and thedam 15, over which it finally spills through the nose ring 11 and entersthe finishing and cooling chambers II5. The finer portions may pass theopenings of the nose ring and fall into the closest set of passages II5.Most of the remainder passes mostly to the remaining passages I|5 andspalls are deflected by the grates |13.

In the above it has been assumed that the burner assembly 3| has beenlighted. This injects fuel, air and recirculating gas into thecarbureting section 5I also entraining air which has risen into thefiring hood from the operations in the stationary shaft 33. Thuspreheated secondary air, as Well as preheated primary air, is obtained,along with injection of hot recirculating gases, the latter having thedesirable effect of properly modulating combustion to avoid producinghot spots.

Referring to Fig. 2, it will be seen that the spent but hot gasespassing through the entering rock in the cone 43 cause this cone to actas a preliminary contact preheater, the temperatures being of the orderof 600 to 900 F. These spent gases have also had their preheating effectin the open section 41 as indicated by the chart. As the stone reachesthe quadrated section of the drum I, it enters a zone of higher preheatpreliminary to calcining, in which the temperature rises until thecaleining zone is reached. A large segment of this calcining zone isconstituted by the quadrated section, the remainder being rin thecarburetting open section 5|. The maximum temperature of 2500 F. or sois reached at the lower region of the quadrated section. In the opensection 5I the temperature is high at the upper end but drops offrapidly toward the dam 15 due to the time required for the gasesproperly to mix and ignite in passing through the section 5I. Since in arotary kiln it is difficult to reach the ideal condition wherein allmaterial is completely calcined before leaving the drum, I cause thematerial to be sent to the stationary shaft 33 for final finishing by aself soaking action supported by the heat carried in the materialitself. Any unfinished nodules have their calcining finished by thissoaking action. As indicated in the temperature chart, the finalfinishing is done With a high, but not the highest, temperature used inthe process. Then as the finished material descends through the chambersI I5, it encounters the cooling zone 4 below the pipes |49, whereinfinishing action ceases, and heat is abstracted by the cooling air, thelatter returning to the drum. This air by-passes the finishing zone 2above the pipes |49 so as not to interfere with the heat-soaking actionrequired in the finishing zone. However, some air is permitted to passthrough the fiinishing zone to carry on the finishing process. Finally,the material reaches a position at the gates IIS where it iscontrollably shaken out into the pressure chamber |39, from whence itescapes through the air lock 39 to the conveyor 4|. In order to maintainthe temperature required in the chambers I I5, these are properlyheat-insulated.

The chart of Fig, 2 shows the percentage of heat transferred to finishedmaterial as progress is made through the apparatus. The largest gain inheat transfer occurs in the calcininf,r zone into which the quadrationof the drum I enters. Heretofore it has not been feasible to enter acalcining zone of a rotary kiln with any similar quadrating structurebecause of the destructive higlitemperatures used v(about'3000 FJ. Inthe present apparatus, the highest- 'temperature is 2500 F., which isconsiderably below the usual practice in rotary kilns, and safe foravailable refractory and insulating materials. This reduction intemperature 'is made possible by the fact that the rotary drumelement isnot used entirely to complete the calcining operation, this being donein the stationary vertical shaft 33, wherein, as the chart discloses, asubstantial additional heatntransfer is effected. The result is that thedrum I may -be :made much shorter since retention timeV is shorter,which tin turn reduces the rather large heat losses associated with longdrums. Moreover, the temperature being lower since cacining is notdriven to the limit in the drum, the hea-t radiating losses are muchlower. The size of the apparatus `for a given capacity is also reduced.

The ordinary rotary kiln requires in excess of 50 cubic feet of clearkiln volume per ton of capacity, and at times as much as 100 cubic feet.The present kiln requires only about 20-30 cubic feet of correspondingkiln space per ton of capacity. This considerably reduces the firstcost, operating and maintenance cost, and radiation heat losses. Inaddition, the thermal 'efficiency is about doubled from about 30% to60%.

Another advantage of carrying the quadrating section into the calciningzone within the drum is that during calcination a thorough tumblingaction is obtained without stratification thus exposing all material toradiant heat. This permits the drum to accept a wider range of stonesizes than heretofore. Hence lthere 'is eliminated ail the apparatususually required for close sizing of stone heretofore required forrotary kilns.

Another advantage of the invention is that a substantial amount ofpreheating is done outside of the drum i, although some preheating isaccomplished in the open section 4l and the upper part of the quadratedsection. Preheating accomplished in the dust chamber by passage of thespent gases through the rock in the cone 93 is more eiiicient and,moreover, has the stated effect of reducing the escaping dust. It is tobe noted in this connection that the spent gases pass through a limitedand uniform stone-bed -thickness, assuring proper gas distribution. Itis to be noted in this connection that Athe by-pass pipe 10| is to takecare'of the condition encountered during shut-down, when stone flow isinterrupted. During such period the bed in the'cone 93 may become chokedwith dust and the by-pass pipe IDI allows operation until vactive stoneflow is again established.

One of the advantages of Ythe use of the stationary shaft 33, which actsas a secondary calciner, is the utilization of the sensible heat of limewhich is discharged by the rotary drum to do additional calcination workoutside of the drum. By means of the present invention, as much as 10%of the total calcination work can be accomplished in this secondarycalciner, which 10% in the ordinary rotary kiln requires about 30% ofthe energy besides requiring large highcost apparatus.

The purpose of the multiple chambers H5 in the shaft 33 is to preventgaseous ilow stratifications. By means of the separate chambers H5,discharge, as well as air admission, can be inde'- pendently controlledto avoid this diiculty.

Over all control is simple, both as to air supply and materialwithdrawal. Control of initial combustion temperatures is obtainedeither by controlling the mixture of 'air and combustibles, orcontrolling the amount of spent gas (CO2) iobtained from therecirculating duct 43. Control over the luminosity of the flame isobtained by creating conditions conducive to cracking of hydrocarbon,that is, creation of stratified flow and retarded access of air to thecombustible gases. However, the present kiln is less dependent on highluminosity of ame, since it contains an abundance of heat-absorbingsurfaces.

In view of the high `temperatures encountered in an ordinary rotarykiln, it is not feasible to insulate them; whereas with the relativelylow temperatures used in the rotary drum herein, insulating material mayIbe Acombined with the refractory lining of the -drum I without dangerof excessive deterioration due to high temperatures.

Air to the cooling zone 4 is regulated in accordance with Vthe limedrawn, and air by-pass of the finishing zone above pipe |49 is regulatedin accordance with the temperature of lime 4leaving the finishing zone.If additional air is needed for combustion in the drum l, this entersthrough the burner assembly 3| or leakage air at the kiln front inducedby vthe general kiln draft created by the exhaust fan 99. This draft isregulated by the thermal orifice established by the dam |09, this beingthe choke, besides preventing rock spillage in the dust chamber.

In view of the above, it will :be seen that the several objects of theinvention are achieved and other advantageous results attained.

As many changes could be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a. limitingsense.

I claim:

1. In a kiln, the combination -of a rotary primary ca'lcining drumsloping from a combination material inlet and gas 'outlet to acombination material 'outlet and fuel inlet, means at the lower end ofthe drum adapted to drop calcined material into several differentstreams of partially calcined material, a stationary vertical shaftlocated at the lower end of the drum having means to determine saidVstreams and having 'an upper hood enveloping the material outlet andthe fuel inlet, said shaft having separate lower compartments adaptedrespectively to receive the different streams of material for furtherand individual 'secondary calcining and cooling, means for withdrawingindividual streams of material from the individual compartments, meansfor introducing cooling air Lto the lower ends of said compart' ments,and means for extracting air from intermediate points of saidcompartments to establish a cooling zone and reintroducing said air intosaid hood whereby self-'calcination may continue in the upper portionsof said compartments, the gaseous product of calcination in said upperportions of the compartments and by-passed air and also fuel from saidfuel inlet passing through the hood into said drum for primary temperedcalcination in the drum in the presence of combustion of fuel.

2. A kiln made according to claim l including means for individuallycontrolling said selfcalcination in said compartments.

3. A kiln comprising a sloping rotary drum of constant diameter`throughout for down-flowing material from an upper open end to a loweropen end and 'for up-'flowing gases from the lower to the upper end,means dividing only a mid- 9 portion of the drum into radially disposedsectors, the ends of which sectors are substantially spaced from therespective ends of the drum to provide unobstructed endwise drumlengths, a burner nozzle adjacent the lower end of the drum adapted toinject a combustible mixture into said lower end, the distance from saidlower end of the drum to one end of the dividing means being substantialand sufficient to allow thorough mixing of said combustible mixturewithout interference from any sectors, in order to provide for efficientcarburetion, the lengths of said sectors being sufficient to effectsubstantial calcination, the unobstructed drum length from the otherends of said sectors to the upper open end of the drum being suicient toeffect a substantial perheating of material approaching the sectors.

4. A kiln comprising a rotary drum having an upper combined materialinlet and gas outlet, a dust 4chamber enclosing said outlet, a rockcontainer in the dust chamber having a rock inlet from the outside and arock outlet pipe leading into said drum, gas passages in the wall of therock container for admitting gas from the dust chamber into the rockcontainer independently of said rock outlet to the drum, whereby asubstantial amount of gas may enter the rock container to pass throughthe rock to settle dust from the entering gas and to preheat the rock,said rock container having an outlet for said gas.

5. A kiln made according to claim 4, wherein said rock outlet pipeleading to the drum is movable in a manner to adjust the position of itsoutlet relative to the inside bottom of the drum.

6. A kiln made according to Claim 4, wherein said gas passages consistof louvers in the rock container and wherein said rock container is ofdownwardly tapered form containing the louvers, and a spreader in thecontainer adapted to spread rock over the louvers in its passage to saidoutlet pipe.

7. In a kiln, a dust chamber having an opening, a rotary calcining drumhaving an end rotary in said opening and introducing hot gases into thedust chamber, a peripheral enclosure around said opening, circularrunning sealing means between said peripheral enclosure and the drum andaxially spaced from said opening, and means other than said opening fordrawing and leading 01T hot gases from said peripheral enclosure, hotgases being supplied to the enclosure by outward flow through saidopening, whereby infiltration of cold outside air to the dust chamber ispositively prevented.

VICTOR J. AZBE.

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